What Is RSV and Why Is It Dangerous?
Respiratory syncytial virus (RSV) is a common respiratory virus that causes mild cold-like symptoms in most healthy adults but can be life-threatening for infants, older adults over 60, and people with weakened immune systems or chronic heart and lung conditions.
RSV infects the lungs and breathing passages and is the leading cause of hospitalization in infants under 1 year of age. In the United States, RSV causes an estimated 58,000-80,000 hospitalizations in children under 5 each year, and 60,000-120,000 hospitalizations and 6,000-10,000 deaths among adults 65 and older annually (Source: CDC, 2024). Nearly all children are infected with RSV by age 2.
The virus spreads through respiratory droplets when an infected person coughs or sneezes, through direct contact (kissing, handshaking), and by touching contaminated surfaces. RSV season in the Northern Hemisphere typically runs from fall through spring, with peak activity in December through February. Unlike some viruses, natural RSV infection does not provide lasting immunity, so reinfection throughout life is common.
RSV was first identified in 1956, and despite decades of research, no vaccine was available until 2023. A disastrous clinical trial in the 1960s in which a formalin-inactivated RSV vaccine caused enhanced disease and two infant deaths delayed vaccine development for over 50 years. Breakthroughs in understanding the RSV F protein structure finally enabled the successful vaccines and antibodies now available.
What RSV Prevention Options Are Now Available?
After decades of failed attempts, effective RSV prevention is now available for the first time. Two vaccines protect adults 60+, a maternal vaccine protects newborns, and a monoclonal antibody protects all infants. These represent a major breakthrough for one of the most significant remaining vaccine-preventable causes of severe respiratory disease.
The FDA approved both Arexvy (GSK) and Abrysvo (Pfizer) for adults 60+ in May-June 2023, and nirsevimab (Beyfortus) for infants in July 2023. Abrysvo is also approved for pregnant women at 32-36 weeks gestation. These products represent three distinct approaches: active vaccination in older adults, passive antibody protection for infants, and maternal vaccination that transfers protective antibodies to newborns before birth.
The CDC's Advisory Committee on Immunization Practices (ACIP) recommended RSV vaccination for adults 60+ through shared clinical decision-making, meaning healthcare providers and patients should discuss individual risk factors rather than vaccinating all older adults universally. This approach reflected the GBS safety signal and the relatively mild course of RSV in many older adults. For infants, nirsevimab is recommended for all babies entering their first RSV season.
Arexvy and Abrysvo were approved by FDA in May-June 2023 for adults 60+
How Do RSV Vaccines Work and How Effective Are They?
RSV vaccines target the fusion (F) protein stabilized in its prefusion form, generating antibodies that prevent the virus from entering cells. Adult vaccines showed 80-89% efficacy against severe RSV disease. Nirsevimab delivers pre-formed antibodies providing immediate 80% protection against RSV hospitalization in infants for approximately 5 months.
The AReSVi-006 trial for Arexvy enrolled over 24,000 adults 60+ and demonstrated 82.6% efficacy against RSV lower respiratory tract disease and 94.1% efficacy against severe disease in the first season. The RENOIR trial for Abrysvo enrolled over 34,000 adults and showed 88.9% efficacy against severe RSV with two or more symptoms. Both vaccines are given as a single intramuscular injection. Second-season efficacy data showed some waning, and revaccination timing is still being determined.
For infants, the MELODY and HARMONIE trials demonstrated that nirsevimab reduced RSV-associated lower respiratory tract infections by approximately 80% and RSV hospitalizations by 77-83%. A single intramuscular injection before or during RSV season provides protection for 5+ months. Real-world data from France, Spain, and the US during the 2023-2024 RSV season confirmed the clinical trial results, with population-level reductions in infant RSV hospitalizations of 50-80% in areas with high uptake.
AReSVi-006 trial showed Arexvy 82.6% effective against RSV lower respiratory tract disease
HARMONIE trial showed nirsevimab reduced RSV hospitalizations by 83%
What Does This Mean for Families and Older Adults?
The availability of RSV prevention products means that families with newborns and adults over 60 now have effective tools to reduce the risk of severe RSV disease for the first time. Understanding eligibility, timing, and the decision-making process helps you take full advantage of these breakthrough options.
For families with newborns, nirsevimab offers straightforward protection. A single injection given before or during RSV season provides approximately 5 months of protection during the period of highest vulnerability. Real-world data from the 2023-2024 season showed dramatic reductions in infant RSV hospitalizations in areas with high nirsevimab uptake, confirming the clinical trial results translate to population-level benefit.
For adults 60 and older, the decision is more nuanced because of the shared clinical decision-making recommendation. Factors that favor vaccination include chronic lung disease (COPD, asthma), chronic heart disease, diabetes, immunocompromised status, living in a nursing home or congregate setting, and being a caregiver for young infants. Talk with your healthcare provider about your individual risk factors.
Cost and access considerations are important. Both adult RSV vaccines are covered by most insurance plans for adults 60+ without out-of-pocket cost under the Inflation Reduction Act's vaccine provisions. Nirsevimab for infants is covered as a routine childhood immunization through the Vaccines for Children program and most private insurance. Supply constraints affected the 2023-2024 season but have largely resolved.
What Questions Should You Ask Your Doctor About RSV?
Whether you are a new parent, an expecting mother, or an older adult, having an informed conversation with your healthcare provider ensures you receive the right RSV protection at the optimal time.
Is RSV vaccination recommended for me based on my age and health conditions? -- For adults 60+, shared clinical decision-making means your doctor will assess your specific risk factors rather than applying a one-size-fits-all recommendation.
I am pregnant — should I get Abrysvo or should my baby receive nirsevimab? -- The choice depends on timing relative to RSV season, gestational age, and individual circumstances. Your OB-GYN and pediatrician can coordinate the best approach for protecting your newborn.
My infant was premature — does that change the RSV prevention recommendation? -- Premature infants are at higher risk for severe RSV and may benefit from nirsevimab even if the mother received the maternal vaccine. Discuss your baby's specific risk profile with your neonatologist or pediatrician.
How do I time RSV, flu, and COVID-19 vaccines together? -- Multiple respiratory virus vaccines can be given simultaneously or spaced apart. Your provider can create a vaccination schedule that optimizes protection before winter respiratory virus season.
